The invention relates to a process for preventing the ripple formation and oxide deposition on the rolled surfaces of a rolled bar from an aluminum alloy, in particular an aluminum/magnesium alloy, during vertical electromagnetic continuous casting using an essentially rectangular inductor and an oxide barrier dipping into the melt head. An installation for carrying out the process also lies within the scope of the invention.
During electromagnetic casting of rolled bars from aluminum/magnesium alloys containing more than about 3% by weight of magnesium defects in the form of vertical ripples and oxide deposits arise on the bar surface, which defects make it necessary to mill over the rolled surfaces of the bars in the case of stringent requirements with respect to the surface quality of rolled products. The cause of the ripple formation and oxide deposits is the high rate of oxidation caused by magnesium at the surface of the aluminum/magnesium alloy melt.
It is known drastically to lower the rate of oxidation by adding beryllium to the metal melt and thus to suppress the surface defects mentioned. However, the addition of beryllium to aluminum alloys is already prohibited in the U.S.A. and a similar ban is also to be expected in other countries in the near future.
U.S. Pat. No. 4,724,896 discloses an installation for reducing the said surface defects in the case of electromagnetic casting of rolled bars by installing an oxide barrier, which is known per se and dips into the melt head and is also known by the technical term of skim dam. The outer edges of the oxide barrier form an angle of between 105 and 150 with the metal melt, as a result of which the radius of the meniscus of the surface of the metal melt is substantially reduced in the zone in contact with the outer edges of the oxide barrier. It is alleged that as a result of this the oxide skin forming on the melt surface breaks away in brief intervals, before the oxide layer has reached the critical thickness for ripple formation and oxide deposition. However, it has been found that even with sloping outer edges of the oxide barrier the surface defects cannot be completely eliminated.